The present invention relates to hydraulic lash adjusters for taking up lash in engine valve trains.
Hydraulic lash adjusters form pivots for cam finger followers, and compensate for dimensional changes in the valve train system of an engine thereby reducing or eliminating the need for mechanical and/or manual adjustment of the valve train. One example of a conventional hydraulic lash adjuster is described and shown in commonly-assigned U.S. Pat. No. 6,039,017 (Hendriksma), the disclosure of which is incorporated herein by reference.
More particularly, conventional hydraulic lash adjusters include a cup-shaped body having a closed end and an open end. A plunger having a closed bottom and an open top is reciprocably disposed within the body such that the closed bottom of the plunger is proximate the closed end of the body. A high-pressure chamber is defined between the closed end of the body and the bottom of the plunger. A piston having an open end and a closed end is also reciprocably disposed within the body. The open end of the piston engages the open top of the plunger during valve opening, and is otherwise spaced a predetermined distance from the plunger. A low-pressure chamber is defined between the plunger and the closed end of the piston. The plunger bottom defines an orifice that extends between the low-pressure chamber and the high-pressure chamber. A check valve associated with the orifice in the plunger controls the flow of fluid between the two chambers. A cam finger follower engages and pivots about the piston body, and exerts thereon a downward force tending to displace the piston in a downward direction relative to the body.
A leak down land is defined by a tight tolerance fit or interface between the outer surface of the plunger and the inner surface of the body. The leak down land provides a path for the flow of oil that is displaced from the high-pressure chamber by the increase in pressure therein due to the force applied to the piston by the associated finger cam follower during a valve opening event. The displaced oil xe2x80x9cleaks downxe2x80x9d into the low-pressure chamber. A support land is defined by the interface between the body and the piston, and as such is coaxial with and axially separated from the leak down land. The support land is necessary to provide a support surface for loads, especially side loads, imposed upon the lash adjuster by the valve train during engine operation.
Space in modern engines is at a premium, and manufacturers are continually striving to reduce the size and weight of component parts, such as hydraulic lash adjusters. Therefore, engine manufacturers are requesting more compact, i.e., smaller and lighter, hydraulic lash adjusters. However, as the size and weight of hydraulic lash adjusters are reduced corresponding degradations in performance and durability are incurred. Such degradations in performance can include a decrease in the load carrying capacity of smaller hydraulic lash adjusters. A reduction in the load carrying capacity of a hydraulic lash adjuster reduces the overall performance of the valve train system.
Therefore, what is needed in the art is a compact hydraulic lash adjuster that has a load carrying capacity that is comparable to the load carrying capacity of conventional/larger hydraulic lash adjusters.
Furthermore, what is needed in the art is a hydraulic lash adjuster that reduces or substantially eliminates the axial separation of the support land and the leak down land.
The present invention provides a compact lash adjuster for taking up lash in engine valve trains.
The invention comprises, in one form thereof, a leak down land and a support land that are substantially cylindrical. The support land is substantially coaxial relative to the leak down land, and at least a portion of the support land is disposed radially opposite the leak down land.
An advantage of the present invention is the lash adjuster is substantially more compact in height or axial dimension than conventional lash adjusters without substantially reducing load carrying capacity.
Another advantage of the present invention is that the support land and leak down land are at least partially radially opposite each other, thereby making the lash adjuster more compact.